Effects of Elevated Fe (III) on Anaerobic Ammonia Oxidation Biofilm Process: Inhibition and Recovery

To investigate the treatment performance of employing the anaerobic ammonia oxidation (anammox) biofilm process to treat the iron-containing industrial wastewater with a low carbon-nitrogen ratio and obtain an optimal condition, the effects of elevated exposure to Fe (III) (ranging from 0 to 1.5 mM) on the anammox biofilm process were explored. The findings indicated that the performance of anammox nitrogen removal remained unaffected when exposed to low levels of Fe (III) (0.1 mM and 0.3 mM). However, high concentrations (higher than 0.5 mM) showed a negative effect. The semi-inhibitory concentration (IC50) of Fe (III) was 1.32 mM. Additionally, under exposure to high levels of Fe (III), a remarkable accumulation of Fe (III) was observed within the anammox system. The total iron concentration increased from 30 mgFe center dot gVSS-1 to a saturation point of approximately 300 mgFe center dot gVSS-1. This accumulation led to a decrease in extracellular polymeric substance (EPS) from 221.4 mg center dot gVSS-1 to 91.3 mg center dot gVSS-1 and specific anammox activity (SAA) from 0.0482 gN center dot(gVSS center dot d)-1 to 0.018 gN center dot(gVSS center dot d)-1. Consequently, the activity of anammox bacteria (AnAOB) was inhibited, leading to a decline in the average total nitrogen removal efficiency (TNRE) from 86.9% to 38.3%. However, it was discovered that the inhibitory effect of continuous Fe (III) could be reversed by introducing the ferric ion complex EDTA center dot 2Na into the system. As a result, the TNRE recovered to 60%. The findings would be useful to optimize the anammox biofilm process by adjusting the concentration of Fe (III) in the practical industrial application.